This invention relates generally to a compact, multiplanar magic-T junction that electromagnetically connects planar waveguides and/or planar transmission lines, while allowing conduction of electrical current or transfer of electromagnetic energy through and between these planar waveguides and planar transmission lines. More specifically, the planar magic-T junction of the current invention contains a difference port that is separated from its other three ports by a ground plane.
In general terms, a magic-T junction consists of a waveguide arrangement with four branches, in which energy is transferred from any one branch into two of the three remaining branches. A signal which enters one branch will divide and emerge from the two adjacent terminal branches, but will be unable to reach the opposite terminal branch.
A waveguide arrangement may consist of one or more planar waveguides and one or more planar transmission lines, with the total number of planar waveguides and planar transmission lines usually not exceeding four. A planar waveguide is formed by a solid dielectric rod or a dielectric filled tubular conductor capable of guiding electromagnetic waves. A planar transmission line for guiding electromagnetic waves generally takes the form of one or more extended, narrow members of uniform width which is commonly designated as a microstrip line when the member is a conducting strip insulated from a single ground plane by a dielectric. The narrow member or members may generally be conductors.
Many microwave and millimeterwave systems utilize planar waveguides and planar transmission lines. The signals from such waveguides are often used in hybrid and monolithic integrated circuits, and are of planar construction.
When planar transmission lines are used in conjunction with planar waveguides, wave energy must be coupled between the associated planar transmission lines and planar waveguides. Prior art techniques for such coupling are illustrated in the following U.S. Patents, the disclosures of which are incorporated herein by reference: U.S. Pat. No. 4,754,239 to Sedivec; U.S. Pat. No. 4,143,342 to Cain et at; U.S. Pat. No. 3,969,691 to Saul; U.S. Pat. No. 3,882,396 to Schneider; U.S. Pat. No. 3,755,759 to Cohn; U.S. Pat. No. 3,732,508 to Ito et al; U.S. Pat. No. 3,579, 149 to Ramsey; and U.S. Pat. No. 3,483,489 to Dietrich.
A magic-T junction is commonly found in microwave and millimeterwave circuit components, and is employed in devices such as amplifiers, power distribution networks and mixers, as disclosed by M. Davidovitz in "A Planar Magic-T Junction with Aperture-Coupled Difference Port," IEEE Microwave and Guided Wave Letters, August 1997, which is incorporated herein by reference. Prior to the present invention, the only magic-T junctions available for use in these and other devices were uniplanar, in that all of the input-output ports leading into these magic-T junctions resided in the same ground plane. This design causes complications such as routing problems, as lines from the input-output ports of the components are forced to cross on the same level. The multiplanar magic-T junction of the present invention overcomes routing problems, and can be easily integrated into microwave and millimeterwave integrated circuits.